This invention is directed generally to the power drive tool arts, and more particularly to a novel lead screw driver tool for installing a threaded fastener in a pilot hole provided therefor in a workpiece.
A number of problems have arisen with respect to the driving of threaded fasteners into pilot holes provided therefor in workpieces, particularly in automotive and other high-volume assembly line types of operations. In such operations, it is important to provide both premolded or partially preassembled parts, and tools which permit the operator to install or assemble parts as quickly and as accurately as possible.
In such applications, untapped pilot holes are generally utilized with tapping or so-called "self-tapping" screws being utilized to engage the untapped hole, thus both tapping and fastening in a single operation. It is important that the self-tapping screw be accurately aligned with the pilot hole prior to the driving thereof, to assure the desired coupling therebetween and to minimize any possible damage or stripping of the pilot hole, which might lead to unreliable engagement. Since the material of the workpiece and pilot hole is often somewhat softer than the material of the screw threads, such alignment is important to avoid such damage to the workpiece and possible unreliability of the resulting assembly.
Similarly, it is important to provide both the proper amount of torque and proper amount of axial advancement or advancing force to the fastener, so that the force of driving can be used both to accurately tap the pilot hole and advance the screw. Importantly, many materials are sufficiently soft and/or brittle, such as the hard, low-tensile strength plastics used in many automobile applications, that an improper axial speed or driving force on the screw will in fact drill out and enlarge the pilot hole rather than form a thread in the annular wall of said pilot hole or aperture.
Advantageously, we have designed a driver tool which avoids the foregoing problems of the prior art. Our novel and improved tool provides means for both assuring proper alignment of the screw and tool with the pilot hole during application of the screw, and also assures the proper speed and force of advancement of the screw relative to the pilot hole, to achieve a reliable threading and engagement thereof, regardless of the nature of the material into which the screw is being engaged.
Our lead screw driver system comprises a drive head for engaging and driving a complementary driver head portion of a threaded fastener, and a manipulator for selectively positioning the drive head and a fastener engaged therewith for alignment of the same for driving the fastener into a pilot hole at a given location in a workpiece. A motor rotates the drive head and a lead screw arrangement is operatively coupled with the drive head for advancing the same at a given rate corresponding to the thread pitch of the fastener to be driven thereby so as to eliminate or minimize the axial stresses upon the material of the workpiece during the driving of the fastener. Preferably, a brake is operatively coupled to the manipulator and this brake is selectively actuatable for holding the manipulator against movement and selectively releasable for permitting movement of the manipulator means, to hold the fastener aligned with the pilot hole while driving the fastener.